The present invention relates generally to laser scanners and, more particularly, to a method and apparatus for sweeping a laser beam in a laser scanner to vary the point of focus of the laser beam such that the depth of field of the scanner is effectively expanded.
Laser scanners for use at point-of-sale checkout counters in supermarkets and other retail stores are becoming more and more common as the reliability of scanners increases and their costs decrease. The scanners are generally mounted within the checkout counters and have upwardly facing windows through which laser beams are projected in defined scanning patterns. A scanning pattern is created by a laser and associated optical components which produce a plurality of intersecting scan lines to define the pattern. A bar coded label including for example a UPC, EAN, JAN or any other code on the packaging of a product presented at a counter is passed through the field of view or scan volume of a laser scanner. Light reflected from the bar coded label is received back through the scanner window and processed to provide identification of the product and pricing information for the sale and other retailing applications such as inventory control.
The depth of field of existing laser scanners, with the exception of holographic scanners, is fixed for any given scan geometry such that the read rate of the scanner is reduced as labels within the field of view are moved from the point of focus of the scanned laser beam. While holographic scanners have variable depth of field and accordingly a substantially uniform read rate throughout the scan volume, holographic scanners are substantially more expensive than other scanners due to the cost of a required holographic element.
It is thus perceived that a need exists for an improved laser scanner having an increased scan volume and a high read rate which is substantially uniform throughout the scan volume comparable to a holographic scanner but at reduced cost to further the utility of laser scanners by continuing the trend of higher performance and lower costs.